Prior to the present invention, various exhaust manifolds and methods of controlling exhaust gases have been disclosed in the prior art. U.S. Pat. No. 2,230,666 which issued Feb. 4, 1941 and is entitled "EXHAUST GAS COLLECTOR" discloses a plurality of laterally spaced exhaust pipes fluidly connected to the cylinders of an associated internal combustion engine open to a diverging funnel-like main exhaust tube providing reduced back pressure and thereby increasing the power of the engine. U.S. Pat. No. 4,288,988 which issued Sep. 15, 1981 and is entitled "METHOD AND APPARATUS FOR IMPROVING THE GAS FLOW IN AN INTERNAL COMBUSTION ENGINE EXHAUST MANIFOLD" discloses a method and apparatus for damping pressure oscillations in the exhaust manifold of an associated engine by throttling the exhaust gas near the outlet of the cylinders and then accelerating the gas flow in the manifold by providing a uniform flow section therein which is substantially smaller than the cylinder bore.
While these and other prior manifold constructions control flow of engine exhaust gas as disclosed, they do not meet the very high performance standards required for compact manifolds and effective manifold operation characterized by low thermal inertia necessary for early light-off of a downstream catalytic converter as now utilized in exhaust treatment in present automotive vehicles. Furthermore, with the advent of crowded engine compartments as found in practically all modern vehicles, these prior designs are generally not suitable because of their bulky configurations.